The present invention generally relates to the reception of digital data transmitted as modulation of selected radio frequency (RF) signals and particularly concerns novel circuitry for reducing errors in the received digital data.
Many signal receivers, including television receivers, designed for receiving data transmitted in a digital format use a double conversion tuner at the receiver front end. The first local oscillator of such receivers typically exhibits a relatively high level of phase noise which, together with other sources of phase noise tends to reduce the eye openings of the demodulated digital data. An excessive level of uncompensated phase noise may thereby contribute to an unacceptable error rate in the demodulated data, especially in the case of a relatively tightly packed data constellation.
In addition, the demodulated data may be degraded by amplitude errors resulting in the data being recovered with undesired offsets and/or at undesired levels of gain. These amplitude-related errors also tend to reduce the eye openings of the demodulated data and, as in the case of phase noise, if left uncorrected may lead to an unacceptable error rate, especially in the case of tightly packed data constellations.
It is therefore a basic object of the present invention to provide an improved system for correcting errors in a demodulated digital data signal.
It is a more specific object of the invention to provide an improved system for reducing the phase noise induced error rate of a demodulated digital data signal.
It is another object of the invention to provide an improved system for reducing amplitude errors in a demodulated digital data signal.
It is a further object of the invention to provide an improved system for rapidly tracking and correcting errors in a demodulated digital data signal.
It is yet another object of the invention to provide an improved system for correcting errors in a demodulated digital data signal in relation to the signal-to-noise (S/N) ratio of the received signal.